FIG. 1 shows a representative prior art closed, multiple blood bag system 10. The system 10 includes a primary bag 12 and transfer bag 14, which are made, e.g., from medical grade plasticized polyvinyl chloride plastic. An outlet port 16 in the primary bag 12 communicates with an inlet port 18 in the transfer bag 14 through an integrally attached length of flexible transfer tubing 20, which is also made from medical grade plasticized polyvinyl chloride plastic. An inlet port 22 in the primary bag 12 communicates with a phlebotomy needle 24 through an integrally attached length of tubing 26. The primary bag 12 contains a suitable liquid anticoagulant 28. A frangible cannula 46 normally blocks liquid flow in the transfer tubing 20 from the primary bag 12 to the transfer bag 14. The system 10 therefore has a "wet" region (i.e., the primary bag 12 filled with liquid anticoagulant 28) and a "dry" (liquid free) region (i.e., the transfer bag 14 and the transfer tubing 20 downstream of the frangible cannula 46.
The system 10 is, before use, closed to communication with the atmosphere. The system 10 is heat sterilized in this closed condition, e.g., using steam. During heat sterilization, the walls of the dry transfer bag 14 and the dry transfer tubing 20 are prone to collapse and sticking together. To prevent this from occurring, conventional practice injects a volume of air or helium into the transfer bag 14 and tubing 20 prior to sterilization. This added step in manufacturing requires additional equipment and increases the labor cost. Furthermore, when the system is ultimately used to process blood, additional steps are often required to transfer or otherwise vent the residual air from the system 10. These air-handling steps can complicate and add to the cost of using the system 10.